docs: def _initialize_integrity_checkers(self, options):
          # type: (Descriptor, blobxfer.models.options.Download) -> None
          """Initialize file integrity checkers
          :param Descriptor self: this
          :param blobxfer.models.options.Download options: download options
          """
          if self._ase.is_encrypted:
              # ensure symmetric key exists
              if blobxfer.util.is_none_or_empty(
                      self._ase.encryption_metadata.symmetric_key):
                  raise RuntimeError(
                      'symmetric key is invalid: provide RSA private key '
                      'or metadata corrupt')
              self.hmac = self._ase.encryption_metadata.initialize_hmac()
          if (self.hmac is None and options.check_file_md5 and
                  blobxfer.util.is_not_empty(self._ase.md5)):
              self.md5 = blobxfer.util.new_md5_hasher()